The Martian Year can be expressed either in Earth Days (It takes 686.9726 Earth days for Mars to complete an orbit of the Sun.) But the Martian Day is different also, about 24 (Earth) hours and forty (Earth) minutes, so a Martian Year is 668.5921 Mars Days.

Mars is between 206 and 249 million km from the Sun, travelling at approximately 24.077 km/sec. Earth is slightly faster (with respect to the Sun), by comparison, at 29.77 km/sec, and it has far less distance to travel around the sun (between 146 and 152 million km).

The Earth and Mars are both planets that orbitround our Star, The Sun. This means they travel round the sun in a circle.

A Year is the time a planet takes to go round the Sun ONCE.

The Earth is nearer to the Sun than Mars. So if you imagine the circle that the Earth makes as it travels round the sun, it is smaller than the circle that Mars makes because Mars is further away from the sun.

Imagine you drive round and round the Indianapolis circuit (which is not quite a circle but pretend it is). Now imagine, at the same time, your friend drives round a smaller circle track on the field INSIDE the real Indianapolis track. His lap times will be much quicker than yours because his lap is much shorter.

Same with Mars and Earth. Mars has a much longer lap than Earth's lap. Mars has further to travel on his big circle. So it takes longer to complete. Almost twice as long.